The present invention relates to a system for non-destructive inspection of structural components.
Non-destructive inspection of the sub-surface region of structural components is particularly important in the industrial sector, e.g., in the aviation industry where especially aircraft outer skin components need to be inspected to monitor their structural integrity. For example, after an accidental damage of an aircraft due to an outside impact, such as a stroke of lightning or a bird strike, it is important to examine the state of the sub-surface region in the respective skin element of the fuselage or wing.
Thus, inspection methods have been developed to inspect sub-surface defects in structural components without inducing damage in the components, and these methods are usually based on a combined use of ultrasonic and thermal monitoring devices.
The basic principle of the combination of ultrasonic and thermal techniques for non-destructive inspection is described in U.S. Pat. No. 6,399,948 and involves an ultrasonic probe that is coupled to a surface of a structural component to be inspected and introduces sound signals into the structural component. These sound signals propagate in an isotropic manner in all directions within the structural component. In case of a defect inside the component, the sound waves are damped through friction in the defect region. This friction results in a generation of heat at the location of the defect, i.e., a conversion of ultrasonic energy into thermal energy takes place at the position of the defect. The resulting thermal radiation can be detected with a sequence of thermal images generated with a thermal imaging camera from outside thus indicating the location of the sub-surface defect within the structural component.
U.S. Pat. No. 6,593,574 describes a similar device for the detection of sub-surface defects in a structural component by means of thermal imaging of the component while ultrasonically waves are excited in the component. This device also includes a hand-held sound “excitation gun” which comprises elongated legs for stabilizing its position and a thermal imaging camera. The sound excitation and the thermal imaging camera are controlled by a control unit for timing purposes.
U.S. Pat. No. 6,795,784 B1 further discloses a method for a non-destructive inspection of the sub-surface region of a component employing an imaging technique during which a superposition of an infrared image of the defect onto a live image of the structural component is used.
However, the prior art is characterized by a high initial energy input into the component to be inspected to effect a significant temperature increase at defects. Such a high energy input may result in damages in the component to be inspected at least at the position where the ultrasonic sound source is located. Further, a reduced energy consumption of the devices employed in the method of interest is desirable to facilitate the use of a cordless device to make the use more comfortable.